Both the Xpress HDSC Series - HD18SCA 2008 and the Xpress SV20SC 2009 are modified-V designs, both built in aluminium, so the buying decision usually comes down to a handful of practical questions: how many people are you putting on the water, how far do you trailer, and what does your tow vehicle weigh?
On paper these two are close siblings in the size department - Xpress HDSC Series - HD18SCA 2008 at 18,0 ft versus Xpress SV20SC 2009 at 20,0 ft. At 1 159 lbs and 1 190 lbs respectively, both sit in a similar weight class - either should pair comfortably with most mid-size SUVs and half-ton trucks, though always confirm your specific tow rating with the motor added.
Both boats share a closely matched power ceiling - 115 hp for the Xpress HDSC Series - HD18SCA 2008 and 115 hp for the Xpress SV20SC 2009. Real-world performance will come down more to which motor is actually bolted on, its load at the time, and whether it's a 4-stroke or 2-stroke setup.
For family outings this is probably the sharpest distinction between the two. The Xpress HDSC Series - HD18SCA 2008 is rated for 6 passengers, while the Xpress SV20SC 2009 caps at 5. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Xpress HDSC Series - HD18SCA 2008 could be the deciding factor.
Bottom line: Choose the Xpress HDSC Series - HD18SCA 2008 if your priority is putting more people on the water - it handles 6 passengers and at 18,0 ft it has the deck room to back that rating up comfortably. The Xpress SV20SC 2009 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 5 that costs less to run day-to-day.